Double glazing company certs etc

[windymill]

Hi, I feel really stupid now. I've had old wooden double glazed windows, doors, and porch replaced over last 18mths, done in three stages. Company, that came through friend, said they would provide guarantees at end of stage 2 for all windows and doors and stage three for porch. Now payment for porch is due, that was completed last week. I paid first two stages by cheque on last day of installation. I asked for invoice and guarantees as told previously and would then pay by backs. Company has given me hand written invoice on headed paper, but not dated. A general copy of window energy rating, but no guarantee for window glazing or frames.
Other info-I chose not to have vents put in, as some of my old windows had them and some didn't, and company said I didn't have to have them. I have also had some problems with inside finishing of sealant, awfully thick, was redone but now have gaps, also nicks in coloured coating, on outside window sill and a couple of frames that I haven't mentioned yet. I don't think company is Fensa registered.
I am now quite worried as to whether I will get any guarantee, or what company has to provide. It all sounds quite dodgy now! Company has repeatedly asked for payment in last week. Though I am not going to pay until I get the right documents but not sure exactly what these should be! Please can anyone advice what I should receive. Thank you.

 

[DHFrames]

Was there a contract including payment plan?
Are the company Fensa or Certass registered?
All installations should be certified within a month of the install date. (2 weeks for Fensa)
Windows being fitted 18 months ago and still not signed off tells me they are not Fensa reg.
Start asking questions.
If they have a Facebook page start there